The best thing to do is go into Menu, Support and then select the option for a reset.
Reset the TV and then see if you get the same fault.
If this hasnt worked it suggests it may well be a hardware failure.
Let me know how you get on.
If you have performed a factory reset and its not displaying the HDMI signal this will be due to a hardware fault.
I assume you are seeing this fault using a number of HDMI cables in different HDMI sockets rather than the same HDMI port (as though the cable may work in a different TV it is sometimes possible the fault is due to the cable).
Once your sure its not the cable (and is present over different HDMI cables), your then into fault finding on the PCB it is most likely the T-Con board.